Conventionally, an A/D converter using delay time, which changes depending on an operating voltage or an operating current, of a delay cell and a technique to use the A/D converter to control an output voltage of a power supply circuit have been disclosed. A delay line A/D converter using a delay cell is preferable for reducing power consumption.
For example, a configuration to detect a difference between delay time of signal propagation of a delay cell column biased by an input voltage to be A/D converted and delay time of signal propagation of a delay cell column biased by a reference voltage and to obtain a digital output has been disclosed. However, delay time of a delay cell also changes, for example, due to temperature. Due to a change in delay time of a delay cell in a delay line A/D converter, an output on a side of a delay cell column, which is to be a reference, varies. Thus, a digital output signal varies according to the change in temperature. For example, when an A/D converter is used to control an output voltage of a power supply circuit, there is a problem in that the output voltage of the power supply circuit varies in response to a variation in an output signal of the A/D converter.